Layouts should be grouped into categories in the IPE

One thing I'll note is that when Layout categories land in the backend...

I'm not sure what you mean by this, but all layouts have categories already per layout_plugin! Or is this just about the extra server-side support in the IPE that this'll need?

Awesome work, Sam!

I tested switching between the Panels layouts, which have no settings, and it all worked fine. I installed the 'layout_plugin_example' module which has an example layout with settings, and that worked great too!

However, there were still some problems with the Display Suite layouts: the settings are saved fine, and can be editted fine, but the layout isn't rendering right. I'm not sure what's going on, but it's almost like the IPE wrappers are added, but the actual layout markup isn't?

The code looked great! Here's some quick review:

1. +++ b/panels_ipe/src/Form/PanelsIPELayoutForm.php
   @@ -0,0 +1,233 @@
   +    // For each block, set the region to the first available region.
   +    foreach ($panels_display->getRegionAssignments() as $region => $region_assignment) {
   +      /** @var \Drupal\Core\Block\BlockPluginInterface $block */
   +      foreach ($region_assignment as $block_id => $block) {
   +        $block->setConfigurationValue('region', $first_region);
   +        $block_config = $block->getConfiguration();
   +        $panels_display->updateBlock($block_id, $block_config);
   +      }
   +    }
   

   It would be nice if it skipped reassigning blocks that were in regions where the same region name exists on the new layout too.

   Most layout collections (Display Suite, Radix Layouts, etc) use consistent names for the regions in all their layouts, so that converting from one to the other will do something sane (ie. switching from sidebar on the left, to sidebar on the right).

   Of course, this breaks down when switching to layouts outside of the same collection, but it's a nice feature if your site is only using one set of layouts.

2. +++ b/src/Plugin/DisplayVariant/PanelsDisplayVariant.php
   @@ -161,6 +161,24 @@ class PanelsDisplayVariant extends BlockDisplayVariant {
   +  public function setLayout($layout_id, $layout_settings) {
   +    $this->configuration['layout'] = $layout_id;
   +    $this->configuration['layout_settings'] = $layout_settings;
   +    $this->layout = $this->layoutManager->createInstance($layout_id, $layout_settings);
   +    return $this;
   +  }
   

   We're also adding a similar function in #2631854: Create PanelsDisplayManager and improve API for making working with PanelsDisplayVariants easier. I don't know which one will get merged first, but it'd be great if they were consistent, and that issue has put a lot of thought into the API (since it's a "make a better Panels API" issue :-)).

   Could you copy the implementation for this function from that issue?

Hrm. Following up on the Display Suite layout issues: they started working for me after a 'drush cr', and now I can't reproduce the problem. So, that might have just been a fluke on my system? If someone else tries the Display Suite layouts and doesn't have any issues, then we can probably write that one off to user error. :-)

Tested #12 and everything works great! Code looks good too! RTBC'd :-)